This invention relates to air cooling apparatus for plastic film that emerges in tubular form from a heated die.
It is well known to employ various combinations of guiding surfaces and air cooling orifices for simultaneous cooling and control of the blown film tube, and to use traveling air cushions of cooling air to prevent the hot plastic from adhering to guiding surfaces in advance of further air cooling. Reference is made for instance to U.S. Pat. Nos. 2,641,022; 3,307,218; 3,307,219; 3,548,042; 3,568,252; 3,577,488; 3,754,067; 3,775,523; 3,835,209; 3,867,083; to British Patent Specification No. 1,045,899; and to the "Dual Cool" air ring described in the commercial literature.
Such arrangements have operated with varying degrees of success. But in respect to each, certain drawbacks are also perceived. With some designs the problems relate to difficulty in adapting a given standard unit to the varying conditions found in the field. Such varying conditions relate, for example, to the different resins employed, the different tube sizes and film gauge thicknesses desired, and the particular different techniques with which personnel of different film production facilities are familiar. Other designs suffer from mechanical complexity or have involved a compromise in either the objective of high production capacity or of ease of start-up and operation.